This application is based on Japanese Patent Application 2000-88874 filed on Mar. 28, 2000, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a magnetoresistive head, a manufacture method thereof, and a magnetic recording/reproducing apparatus with such a magnetic head.
b) Description of the Related Art
Magnetic recording/reproducing apparatus such as hard disk drives are rapidly reducing their sizes and increasing recording densities. The recording track width of a recording medium is becoming narrower than ever to improve the recording density.
In order to compensate for a reproduction output level lowered by a narrower width of a recording track, a magnetoresistive head (hereinafter abbreviated to xe2x80x9cMR headxe2x80x9d) having a high sensitivity has been developed. Recently, an MR head capable of obtaining a large output signal by utilizing a giant magnetoresistance effect (hereinafter abbreviated to xe2x80x9cGMRxe2x80x9d) is practically used.
An MR head utilizing GMR uses a multi-layer magnetic film (spin valve film) formed, for example, by sequentially stacking a ferromagnetic layer (free layer) whose magnetization direction is changed with an external magnetic field, a non-magnetic conductive layer, a ferromagnetic layer (pinning layer) whose magnetization direction is pinned down, and an antiferromagnetic layer for pinning the magnetization direction of the pinning layer.
It is important to suppress Barkhausen noises of an MR head using a spin valve film to be generated by discontinuous motion of magnetic domain walls in the free layer. The structure of efficiently applying a longitudinal magnetic field to the free layer has been adopted to suppress Barkhausen noises.
Typical examples of the longitudinal magnetic field applying structure are an abutted junction structure such as disclosed in JP-B-7-122925 and a gull wing structure such as disclosed in JP-A-11-86237 in which this structure is called an overlaid structure.
FIG. 13 shows an MR head having the abutted junction structure shown in JP-B-7-122925.
An MR head 40 shown in FIG. 13 has an MR film 43 and a pair of hard magnets for applying a longitudinal magnetic field to the MR layer 43. The MR film 43 is formed on a lower gap layer 42 formed on a lower shield film 41 on a substrate (not shown). Each hard magnet is constituted of a magnet film 44 formed on the lower gap layer 42 and an electrically conductive film 45 formed on the magnetic film 44.
This MR head 40 constructed as above is manufactured in the following method. An MR film is deposited and a mask is formed on the MR film to remove an unnecessary portion thereof by milling and form the MR film 43. Then, the magnet film 44 is deposited on the exposed surface of the lower gap layer 42 and the conductive film 45 is deposited. Lastly, the mask is removed by lift-off. A reading track width TW is equal to the space between opposite ends of the pair of hard magnets of the MR head 40.
The MR film 43 of the MR head 40 formed by milling has a forward tapered side wall 43a depending upon a milling angle and a shadowing effect of oblique milling. Therefore, the side wall 44a of the magnet film 44 for applying a longitudinal magnetic field to the MR film 43 has a backward tapered shape. In order to narrow a reading track, the ferromagnetic layer (free layer) of the MR film 43 is formed to have the upper narrowed tapered portion, and the MR film 43 becomes in contact with the magnet film 44 only at its side walls 43a. 
Therefore, the magnet film 44 gives the MR film 43 a magnetic effect only or dominantly of a static magnetic field. This poses the problem that a single domain cannot be formed efficiently in the MR film 43. Another problem is unstable electrical conduction between the MR film 43 and conductive film 45 because they contact only at the side walls 43a. Another problem is burs formed on the edges of the magnet film 44 or conductive film 45 when the mask used for milling is lifted off. Burs near the free layer make the gap thickness of the MR head irregular. Therefore, signal separation between adjacent bits in a recording medium becomes imperfect, or at the worst, the magnet film 44 and an upper shield layer to be formed at a later process may be short-circuited.
FIG. 14 shows an MR head having the gull wing structure such as shown in JP-A-11-86237.
An MR head 50 shown in FIG. 14 has a lower shield film 51 formed on a substrate (not shown), a lower gap layer 52 formed on the film 51, a pair of hard magnets formed on the lower gap layer 52 and an MR film 55. Each of the hard magnets is constituted of a magnet film 53 formed on the lower gap layer 52 and an electrically conductive film 54 formed on the magnet film 53. The magnet film 53 applies a longitudinal magnetic field to the MR film 55.
In manufacturing the MR head 50 constructed as above, a magnet film and a conductive film are laminated and portions thereof corresponding to the reading track width TW are removed by milling to form the magnet film 53 and conductive film 54. Thereafter, an MR film is deposited and an unnecessary portion thereof is removed to form the MR film 55. The reading track width TW is equal to the width of a contact region of the MR film 55 with the lower gap layer 52.
Since the MR film 55 of the MR head 50 manufactured by this method is in surface contact with the magnet film 53 and conductive film 54, electrical conduction therebetween is more reliable than the MR head 40 having the abutted junction structure. Since the side walls of the magnet film 53 on the MR film 55 side have the forward tapered shape, a single domain can be formed in the MR film 55 by positively using not only the static magnetic field applied by the magnet film 53 but also exchange coupling at the interface between the magnet film 53 and MR film 55.
For mass production of MR heads, generally a number of MR heads are formed at a time on a single large area substrate, and each MR head together with a partial region of the large area substrate is cut from the substrate.
With this method, a variation in thicknesses of each film formed on the whole area of the large area substrate becomes a variation in reading track widths TW of MR heads 50 under mass production. The reason for this will be described with reference to FIGS. 15A to 15C.
FIGS. 15A to 15C are schematic cross sectional views illustrating the manufacture processes for the MR films 55 of the MR heads 50.
A film to be used for the magnet films 53 is formed, for example, by depositing a CoCrPt alloy layer (60 nm in thickness) on an underlying film (20 nm in thickness) of Cr. A film to be used for the conductive films 54 is formed, for example, by depositing a Ta alloy layer (200 nm in thickness) on an underlying film (20 nm in thickness) made of Ti. The thickness of the magnetic film 53 and conductive film 54 (a thickness of as great as 300 nm in total) formed on the lower gap layer 52 has inevitably a variation.
FIG. 15A shows a thin portion X and a thick portion Y of a laminated film of the magnet film 53 and conductive film 54.
A variation in film thicknesses is generated because of different film forming rates in each area of a large area substrate. For example, a variation in film forming rates is suppressed by rotating a substrate relative to the target in a sputtering system. However, there is no film forming system for mass production which has the same film forming rate in the whole area of a large area substrate. A film thickness difference in the whole area of a large area substrate becomes larger as the thickness of a film becomes greater.
As shown in FIG. 15B, when the conductive film 54 and magnet film 53 in the thin portion X is trenched by milling and the low gap layer 52 is exposed, the lower gap layer 52 in the thick portion Y is not still exposed. In FIG. 15B, reference symbol 54a represents a mask used for milling.
FIG. 15C shows the state of each film when milling continues after the state shown in FIG. 15B.
As shown, as milling continues, the conductive film 54 is trenched and the lower gap layer 52 in the thick portion Y exposes. In the thin portion X, the lower gap layer 52 is trenched so that the reading track width TW is broadened. From this reason, there is a variation in reading track widths TW of MR heads 50 formed by mass production.
FIG. 16 is a schematic diagram illustrating a variation in reading track widths of MR heads 50 formed by mass production.
A general sputtering system was used to deposit a Cr film (20 nm in thickness)/a CoCrPt alloy layer (60 nm in thickness)/a Ti film (20 nm in thickness)/a Ta alloy layer (200 nm in thickness), and milling was performed to form a lamination film ML of a magnetic film and an electrically conductive film on the lower gap layer 52.
A variation in reading track widths TW was calculated as in the following on the assumption that a tip angle xcex8 of the lamination film ML was 20 degrees (xcex8=20xc2x0) and that a variation t in average thicknesses of the lamination films ML on a large area substrate was about xc2x13%.
Since the total film thickness T of the lamination film ML is 300 nm, the variation t in film thicknesses is 18 nm (t=0.03xc3x972xc3x97300 nm) at a maximum. A variation in tip positions of the lamination films ML is 49.5 nm (TW1=18 nm/tan 20xc2x0) on one side (TW1). As this variation is converted into a variation in reading track widths TW, the reading track width variation is doubled to 99 nm (2TW1) which is about 0.1 xcexcm.
This calculation is assumed that a variation in milling precisions in in-plane is zero. Therefore, an actual variation is larger than 0.1 xcexcm. Such a variation cannot be permitted for the manufacture of thin film magnetic heads compatible with narrow tracks.
In order to reduce a variation in film thicknesses of the magnet film 53 and conductive film 54, it is desired to thin these films as much as possible. However, as the conductive film 54 is thinned, the electric resistance thereof other than the MR film 55 is increased so that the MR ratio (=xcex94R/R) lowers and the reading-out sensitivity is lowered. To solve this, an MR head having a gull wing lead-overlaid structure such as shown in JP-A-11-86237 has been proposed which is an improved MR head of the gull wing structure.
FIG. 17 shows an MR head 60 of the gull wing lead-overlaid structure proposed in JP-A-11-86237.
As shown, an MR head 60 has a lower gap layer 62 formed on a lower shield film 61 on a substrate (not shown), and a pair of magnet films 63 formed on the lower gap layer 62. There is a recess of an inverted trapezoid shape between the pair of magnet films 63. An MR film 64 is formed extending from the bottom of the recess to the surfaces of the magnet films 63. A pair of electrically conductive films (overlaid electrodes) 65 covers the magnet films 63 and MR film 64, the conductive films facing each other over the bottom of the recess.
The pair of magnet films 63 is formed by depositing a magnet film and forming the recess through this film. The side wall of each magnet film 63 on the recess side has a forward tapered shape. A film to be used for forming the MR film 64 is deposited on the pair of magnet films 63 and recess and an unnecessary portion thereof is removed to form the MR film 64. A film to be used for forming the conductive films 65 is deposited on the MR film 64 and on the pair of magnet films 63, and an unnecessary portion thereof is removed to form the pair of conductive films (overlaid electrodes) 65.
The overlaid electrodes 65 of the MR head 60 extend to the inside of the recess from the tips 63a and 63b of the magnet films 63. The reading track width TW is therefore determined by a distance 65a (TW=65a) between the pair of overlaid electrodes 65. Even if there is a variation in distance (recess bottom width) 63c between tips of the pair of magnet films 63, this variation will not substantially influence the reading track width TW.
However, the thickness of the upper gap layer of the MR head 60 is likely to become irregular, because of a relatively large step between the surface of the MR film 64 and the upper surfaces of the overlaid electrodes (conductive films) 65.
FIG. 18 shows an MR head 60 with an upper gap layer 66. As shown, the upper gap layer 66 is formed on the MR film 64 and the pair of overlaid electrodes 65. Since there is a relatively large step between the surface of the MR film 64 and the upper surfaces of the overlaid electrodes 65, the thickness of the upper gap layer 66 in the reading track width TW may become not uniform.
In reading a signal from one bit in a recording medium, it is desired to pick up this signal at a high output level and eliminate the adverse effect of a signal which may be read at the same time from an adjacent bit. It is desired therefore to make uniform the gap thickness corresponding to the thickness of the region sandwiched between the upper and lower shield layers over the whole area (whole reading track width) of the free layer of the MR head. Since the thickness of the upper gap layer 66 of the gull wing lead-overlaid structure is not uniform, the gap thickness is likely to become irregular. Separation of a signal read-out from a recording medium from garbage unwantedly read-out from the recording medium is therefore likely to become imperfect.
The pair of overlaid electrodes 65 is generally formed through photolithography. It is therefore difficult to form the pair of overlaid electrodes 65 to have a predetermined distance, i.e., a distance corresponding to the reading track width TW therebetween.
As shown in FIG. 19, in forming a pair of overlaid electrodes 65, an electrically conductive film 65c is first deposited and resist 67 is coated on this film 65c. The resist 67 is partially exposed in the area corresponding to the space to be formed between the pair of overlaid electrodes 65. The resist 67 is developed to remove the resist 68 exposed to light. By using the left resist 67 as a mask, the conductive film 65c is etched by milling.
The conductive film 65c under the resist 67 have slanted surfaces. Since exposure light reflects at this slanted surface during the exposure, it is difficult to expose a predetermined pattern so that a variation in reading track widths TW is likely to occur.
The positions of the pair of overlaid electrodes 65 shift inevitably in accordance with an alignment precision (e.g., 0.5 xcexcm) of an exposure system to be used for photolithography.
FIG. 20 shows an example of the positions of a pair of overlaid electrodes 65 shifted from desired positions.
Opposite ends 65a and 65b of the overlaid electrodes 65 are required to be positioned in the bottom width 63c of the recess formed between the right and left magnet films 63. In order to form the overlaid electrodes at predetermined positions, it is necessary that the bottom width 63c of the recess have a size larger than a value of the alignment precision of an exposure system.
As the bottom width 63c of the recess becomes broader, a static magnetic field effect of the magnet films 63 to the MR film 64 is weaken and a single domain is difficult to be formed in the MR film 64.
In order to positively utilize the MR ratio of the MR film 64 of the gull wing lead-overlaid structure and obtain a high reading-out efficiency, it is desired to lower the electrical resistance of components other than the MR film 64 as much as possible. However, if the overlaid electrodes 65 are made thicker to lower the electrical resistance thereof other than the MR film 64 of the gull wing lead-overlaid structure, irregularity of the gap thickness increases further or the overlaid electrodes become difficult to be formed.
It is an object of the present invention to provide a magnetoresistive head having the structure that the head is compatible with narrow tracks and that the reading-out sensitivity of each head formed by mass production can be easily prevented from being lowered and the uniformity of a reading track width of each head can be easily prevented from being lowered.
It is another object of the present invention to provide a recording/reproducing magnetic head having the structure that the head is compatible with narrow tracks and that the reading-out sensitivity of each head formed by mass production can be easily prevented from being lowered and the uniformity of a reading track width of each head can be easily prevented from being lowered.
It is still another object of the present invention to provide a method of manufacturing a magnetoresistive head having the structure that the head is compatible with narrow tracks and that the reading-out sensitivity of each head even under mass production can be easily prevented from being lowered and the uniformity of a reading track width of each head can be easily prevented from being lowered.
It is a further object of the present invention to provide a magnetic recording/reproducing apparatus provided with a recording/reproducing magnetic head having the structure that the head is compatible with narrow tracks and that the reading-out sensitivity of each head even under mass production can be easily prevented from being lowered and the uniformity of a reading track width of each head can be easily prevented from being lowered.
According to one aspect of the present invention, there is provided a magnetoresistive head, comprising: a lower shield layer formed on a substrate and made of soft magnetic material; a lower gap layer formed on said lower shield layer and made of insulating material; a pair of magnet films formed on said lower gap layer at a predetermined distance therebetween, said pair of magnet films defining a recess on said lower gap layer, the recess having generally an inverted trapezoid shape in cross section; a magnetoresistive film covering a bottom and side wall of the recess and partial upper surfaces of said pair of magnet films; and a pair of electrically conductive films, one of which is formed on one magnet film of said pair of magnet films and the other is formed on the other magnet film of said pair of magnet films, and being in contact with said magnetoresistive film only at a position outside of the recess.
According to another aspect of the present invention, there is provided a recording/reproducing magnetic head comprising: a reading-out magnetic head including (i) a lower shield layer formed on a substrate and made of soft magnetic material, (ii) a lower gap layer formed on said lower shield layer and made of insulating material, (iii) a pair of magnet films formed on said lower gap layer at a predetermined distance therebetween, said pair of magnet films defining a recess on said lower gap layer, the recess having generally an inverted trapezoid shape in cross section, (iv) a magnetoresistive film covering a bottom and side wall of the recess and partial upper surfaces of said pair of magnet films, (v) a pair of electrically conductive films, one of which is formed on one magnet film of said pair of magnet films and the other is formed on the other magnet film of said pair of magnet films, and being in contact with said magnetoresistive film only at a position outside of the recess, and (vi) an upper gap layer made of inorganic insulating material and covering said magnetoresistive film and said pair of electrically conductive films; and a writing head formed on said reading-out magnetic head, said writing head being an induction type magnetic head.
According to another aspect of the present invention, there is provided a method of manufacturing a magnetoresistive head, comprising: a preparing step of preparing a substrate including (i) a lower shield layer made of soft magnetic material, (ii) a lower gap layer formed on said lower shield layer and made of insulating material, (iii) a pair of magnet films formed on said lower gap layer at a predetermined distance therebetween, said pair of magnet films defining a recess on said lower gap layer, the recess having generally an inverted trapezoid shape in cross section, and (iv) a magnetoresistive film covering a bottom and side wall of the recess and partial upper surfaces of said pair of magnet films; and an electrically conductive film forming step of forming a pair of electrically conductive films, one of which is formed on one magnet film of said pair of magnet films and the other is formed on the other magnet film of said pair of magnet films, and being in contact with said magnetoresistive film only at a position outside of the recess.
According to another aspect of the present invention, there is provided a magnetic recording/reproducing apparatus, comprising: a magnetic recording medium; a magnetic head driving unit for rotating forward or backward rotating a rotary shaft; an arm mounted on the rotary shaft and moving along an arc path over said recording medium when driven by the rotary shaft; a suspension mounted on a front end of said arm; and a recording/reproducing magnetic head mounted on said suspension, said recording/reproducing magnetic head including: a reading-out magnetic head including (i) a lower shield layer formed on a substrate and made of soft magnetic material, (ii) a lower gap layer formed on said lower shield layer and made of insulating material, (iii) a pair of magnet films formed on said lower gap layer at a predetermined distance therebetween, said pair of magnet films defining a recess on said lower gap layer, the recess having generally an inverted trapezoid shape in cross section, (iv) a magnetoresistive film covering a bottom and side wall of the recess and partial upper surfaces of said pair of magnet films, (v) a pair of electrically conductive films, one of which is formed on one magnet film of said pair of magnet films and the other is formed on the other magnet film of said pair of magnet films, and being in contact with said magnetoresistive film only at a position outside of the recess, and (vi) an upper gap layer made of inorganic insulating material and covering said magnetoresistive film and said pair of electrically conductive films; and a writing head formed on said reading-out magnetic head, said writing head being an induction type magnetic head.
A reading track width TW of the magnetoresistive head (MR head) constructed as above can be substantially defined when the pair of magnet films is formed on the lower gap layer, whereas the reading track width TW of a conventional MR head is defined when a pair of electrically conductive films thicker than the magnet films is formed. Therefore, a variation in reading track widths TW of MR heads even under mass production can be easily reduced, and compatibility with narrow tracks can be easily realized.
Since the magnetoresistive film (MR film) and conductive films contact at the positions outside of the recess defined on the lower gap layer by the pair of magnet films, a precision of the reading track width TW does not depend upon the thickness of the conductive films so that the conductive film can be easily made thick. Since the good electrical conductivity can be established between the MR film and conductive films, MR heads having a high reading-out sensitivity can be easily mass-produced.
Since the conductive films do not extend to the inside of the recess, even if the upper gap layer is formed on the MR film, a variation in thicknesses of upper gap layers formed on the MR films can be reduced. A variation in gap thicknesses of MR heads even under mass production can be reduced. MR heads capable of separating a signal read-out from a bit of a recording medium from garbage unwantedly read-out from the recording medium can be manufactured easily.